Recently, packet forwarding has increasingly been applied to the field of telecommunications carriers with advances in packet technology. The predominant network configuration is a ring network, which is advantageous in terms of wiring efficiency and fault bypass. In particular, ring networks based on label switching such as multiprotocol label switching (MPLS) have been widely applied.
The application of packet forwarding to the field of telecommunications carriers requires high reliability. As means for bypassing a fault, fault bypass techniques similar to unidirectional path-switched ring (UPSR) and bidirectional line-switched ring (BLSR), which are standard for synchronous digital hierarchy (SDH) and synchronous optical network (SONET), have also been proposed for MPLS networks.
For BLSR, when a fault occurs in a working path, traffic (packets) is rerouted to a backup path set to be opposite in direction to the working path in a bidirectional ring. Therefore, no traffic (packets) flows through the backup path before a fault occurs.
A related technique is disclosed in Japanese Laid-Open Patent Publication No. 2005-217904.